1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer. More particularly it pertains to a process for efficient stable continuous production of a styrenic polymer in which the stereochemical structure of the main polymer chain is of high degree of syndiotactic configuration.
2. Description of Related Arts
Heretofore, styrenic polymers of atactic configuration in its stereochemical structure that are produced by the radical polymerization method have been molded to various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding, cast molding or the like, and widely used as domestic electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials. However, such styrenic polymers of atactic configuration have suffered the disadvantages of inferior heat resistance and chemical resistance.
The group of the present inventors recently succeeded in the development of the styrenic polymers having a high degree of syndiotactic configuration, and further demonstrated that the styrenic polymers of syndiotactic configuration were obtained by the use of a catalyst comprising a titanium compound and a contact product (alkylaluminoxane) between an organoaluminum compound and a condensation agent or a catalyst comprising a transition metal compound and a coordination complex compound composed of a cation and an anion in which a plurality of radicals are bonded to a metal. (Refer to Japanese Patent Application Laid-Open No. 187708/1987).
As a process for continuously producing a styrenic polymer in powdery form having such syndiotactic configuration, for example, Japanese Patent Application Laid Open No. 191,609/1990 discloses a polymerization method in which a styrenic monomer as the starting material together with a catalyst is fed into a horizontal self-cleaning type reactor.
However, the above-mentioned horizontal self-cleaning type reactor has a high piston flow property as compared with a tank reactor with agitation blades and therefore, causes ununiform distributions of temperature, conversion efficiency, etc. in the axis direction in the reactor, when charging a styrenic monomer as the starting material mixed with a catalyst. Particularly in the case of a methylaluminoxane-based catalyst, an extremely high initial-rate of reaction brings about a violent heat release due to rapid reaction in the vicinity of the feed inlet of a starting monomer and catalyst in the reactor, whereas in the latter half of the reactor the reaction proceeds at a decreasing rate with a reaction heat one-fourth or less as low as that in the first half therein.
As a general means for removing reaction heat in such a type of reactor, there is used a reactor with a cooling jacket with which the reactor is cooled using a coolant such as cooling water. Nevertheless, cooling with a single jacket induces ununiform temperature distribution in the reactor with the result that the first half of the reactor acts as the high temperature zone with much difference in temperature from the jacket, while the latter half thereof acts as the low temperature zone with little difference therefrom. In such a case, a temperature exceeding 100.degree. C. in the high temperature zone is unfavorable from the viewpoint of operation and quality control, since it gives rise to the formation of a styrenic polymer of atactic configuration as well as deterioration of catalyst activity.
As the countermeasure against such a problem, the jacket is divided into multiple sections so as to maintain a uniform temperature in the reactor by supplying each section of the jacket with a coolant at a optimum temperature to regulate the temperatures in the reactor. However, as for a method in which a starting monomer and a catalyst are mixed and fed into the reactor, the high initial-rate of reaction makes it necessary to lower the coolant temperature with a decrease in distance between an jacket section and the feed inlet. An increase in the feed rates of a starting monomer and a catalyst for the purpose of enhancing the productivity increases the reaction heat release and thus, requires to lower the temperature of the coolant to be fed in the jacket section near to the feed inlet. As the result, the coolant temperature finally reaches the lowest possible limit, causing an increase in the temperature in the feed zone with the result that the production increase is no longer possible.
Under such circumstances, intensive research and investigation were made by the present inventors for the purpose of eliminating the above-mentioned problems involved in the conventional technique and developing a process capable of easily controlling the reactor inside temperature and thereby enhancing the productivity in the case where a styrenic polymer having a high degree of syndiotactic configuration is continuously produced by the use of a catalyst system which causes wide variation in the rate of reaction in a horizontal self-cleaning type reactor.
As a result, it has been found by the present inventors that the above-mentioned problem is solved by feeding in a reactor a catalyst or a catalyst and a starting monomer dividedly into at least two portions. The present invention has been accomplished by the aforesaid finding and information.